Particular chemicals in soy, called isoflavones, might offer a number of health benefits, particularly in post-menopausal women. The Memorial Sloan Kettering Cancer Center, however, reports mixed results in studies looking at their effects on various conditions. These substances have weak estrogenic effects, which might offer benefits for menopause, where declining estrogen levels trigger unpleasant symptoms. Consuming isoflavones might also reduce the risk of conditions that result from excess estrogen production. In this instance, the plant estrogens bind to estrogen receptor sites in cells, which prevents the excess estrogen in the body from attaching and exerting its negative effects. On the other hand, the estrogen in isoflavones could prove problematic in some instances, particularly if taken in supplement form. Some concerns exists over the use of isolated isoflavones, and you should talk to your doctor about whether or not it is appropriate to use them to address your health concerns.
According to the University of Maryland Medical Center, the following amounts of soy isoflavones consumed daily have been suggested to address various health concerns: high cholesterol, 50 mg; blood vessel health and lowering blood pressure, 40 mg to 80 mg; bone health, 50 mg; and hot flashes, 40 mg to 80 mg. The University of Pittsburgh Medical Center reports a standard dosage of 40 mg to 80 mg daily, depending on the condition.
Isoflavones and Female Cancers
Estrogen can stimulate the growth of breast cancer and uterine cancer cells. Because of the estrogenic activity of isoflavones, some concern exists over the use of isoflavones if you currently have or have had in the past these hormonally sensitive cancers. According to the UPMC, research indicates the estrogen in soy does not appear to pose the same risks as the estrogen in the body, but stresses that large-scale studies confirming this have not been conducted. For this reason, you should not supplement with isoflavones without talking to your doctor first. They might also reduce the effectiveness of the breast cancer drug tamoxifen.
Other Hormone-Related Concerns
Consuming soy products in normal amounts while pregnant or breastfeeding appears to pose little risk. Excessive consumption however, whether in food or supplement form, could exert a negative hormonal impact on your unborn child. Whether or not soy negatively affects the thyroid gland in individuals with weak functioning has not been clearly established. Some studies found it impaired thyroid function, while others found it exerted no effect or even increased production of thyroid hormone. Soy appears to have a complex effect on thyroid functioning. If you suffer from hypothyroidism, talk to your doctor about whether or not you should supplement with isoflavones.
Besides its potentially negative interactions with tamoxifen, isoflavones might also interact with other medications. Because of the potential to affect absorption of thyroid hormone, you should take isoflavone supplements and your hormone-replacement medication several hours apart, provided your doctor has approved their use. Isoflavones could potentially interact with hormonal contraceptive, but the UPMC notes research suggests they do not. These supplements might also interact with the osteoporosis medication raloxifene.